Lecture - development Flashcards
Embryos consist of three layers of tissue
ectoderm (outermost), mesoderm (middle), and endoderm (innermost).
phases of development
induction of the neural plate; neural proliferation; migration and aggregation; axon growth and synapse formation; and neuron death and synapse rearrangement.
induction of the neural plate
A patch of tissue on the ectoderm becomes the neural plate. This transformation is induced by chemical signals from the mesoderm. Visible three weeks after conception.
embryonic stem cells
neural plate cells. have unlimited capacity for self renewal. can become any type of mature cell.
totipotent
earliest cells have the ability to become any type of body cell
Multipotent
with development, neural plate cells are limited to becoming one of the range of mature nervous system cells
neural crest
A structure dorsal to the neural tube and formed from neural tube cells. Develops into the cells of the peripheral nervous system.
neural proliferation
Neural plate folds to form the neural groove, which then fuses to form the neural tube. The neural tube will become the cerebral ventricles and central canal in the spinal cord. Neural tube cells proliferate forming three swellings: forebrain, midbrain, and hindbrain.
neural migration
Once cells have been created through cell division in the ventricular zone of the neural tube, they migrate to their final destinations to form nuclei and cortical layers. Migrating cells are immature, lacking axons and dendrites.
cortical layers form in an
“inside out pattern.” layer 6 forms first, then 5, 4, etc.
two types of neural tube migration
radial migration and tangential migration. most cells engage in both types.
radial migration
usually by moving along radial glial cells
two methods of migration
somal - caterpillar-like
glial-mediated migration - – cell moves along a radial glial network
neural aggregation
After migration, cells align themselves with others cells and form nuclei.
neural differentiation
Neurons take their adult morphology
myelination
In humans, starts in spinal cord and continues toward forebrain
growth cone
At the growing tip of each axon, the growth cone
extends and retracts filopodia as if exploring to find its way
- blueprint hypothesis (for target finding and synapse info)
pre-formed pathways and tunnels.
- Pioneer growth cones, guidepost cells, fasciculation.
- Role of cell-adhesion molecules (CAM).
- Evidence against: Cells transplanted to other places still find correct targets.
- chemoaffinity hypothesis (for target finding and synapse info)
Connections are
highly specific. Sperry’s eye rotation experiment.
topographic gradient hypothesis
sheets of developing neurons are often charcterized by two intersecting chemical gradients, which can define the localization of each neuron.
- fine-tuning of connections by spontaneous and experience-evoked neural activity (for target finding and synapse info)
- The Hebb postulate: Neurons that fire together, wire together.
- N-methyl-D-aspartate receptors (NMDA receptors) detect correlated activity between pre- and post-synaptic neurons
overproduction
during development many neurons die.
apoptosis
active, programmed cell death
necrosis
passive cell death.
Neurons die due to failure to
compete for neurotrohic factors provided by targets (e.g., NGF, nerve growth factor). the more targets, the fewer cell deaths. destroying some cells increases survival rate of remaining cells.
synapse rearrangemnet
a diffuse pattern of synaptic contact is characteristic of early stages of devleopment. a more focused pattern of synaptic contact is present after synapse rearrangment.
More than 200 genetic mutations
associated with mental retardation
Developing brain is more vulnerable than the mature brain to
malnutrition, toxic chemicals and infections.
Hypothyroidism
induces mental retardation in infants.
fetal alcohol syndrome
Dendrites tend to be short, with few branches
rett syndrome
Anomaly of brain development with mental retardation affecting mainly girls older than 1-2 years. Associated with lack of dendritic development.
